Afghan guerrillas claim to have captured part of the key eastern city of Jalalabad, but the government says the insurgents were routed in their first major offensive since the Soviet pullout.

Government and rebel troops have clashed at Jalalabad since March 6 in the first major test of communist defenses since the Red Army ended its nine-year intervention in Afghanistan one month ago.Official Radio Kabul and the Soviet news agency Tass said Monday that Afghan regime forces had repulsed about 14,000 insurgents and 3,000 "Pakistani advisers" after a week of heavy fighting.

"As a result of the heroism and power of the armed forces, (the insurgents) faced shameful and deadly defeat," the radio said in a broadcast monitored in Islamabad.

Communist sources claimed government troops killed more than 2,000 of the attackers, but guerrillas put their losses at about 100 dead and 400 wounded. Pakistan, which supports the anti-Marxist insurgents, denies it has any combat troops in neighboring Afghanistan.

The guerrillas, called mujahedeen or "holy warriors," said Monday they had captured Jalalabad's key garrison at Samarkhel, breached part of the airport perimeter and were holding the old section of the city.

They claimed to have captured about 700 regime troops, most of them from Samarkhel.

Ghaus Amer of the Afghan News Agency, an organ of hardline guerrilla leader Gulbaddin Hekmatyar, Tuesday described a lull in fighting the previous 24 hours as a change of tactics: "The mujahedeen are now switching to increase the siege of the city to avoid further bloodshed."

It was not clear whether the insurgents were preparing an immediate second attack.

Correspondents and other eyewitnesses arriving in Pakistan have described intense aerial shelling of mujahedeen positions between Jalalabad and the border, 33 miles to the east.

The capture of Jalalabad, a city of about 200,000, would be a crucial moral victory for the guerrillas, who are fighting to establish an Islamic republic of Afghanistan.